I have been using Silmar 249 polyester resin for some overlay work and have experienced some cloudiness after cure on a couple of parts.
I’m not sure what causes this? I am in Utah and humidity is non existent so that cant be a factor. It doesn’t seem to be in every layer of poly so maybe it’s an issue with over catalyzing the resin? Or could it be from not letting the previous layer cure long enough before adding the next coat?
Also how long am I required to wait between coats? I have been adding the next layer when the previous one is just a bit tacky but does not stick to my finger.
You’re not putting surfacing wax in each resin batch, are you?
I usually follow the “tacky but does not stick” protocol myself…haven’t had any cloudiness issues yet.
I’m not adding surfacing wax until the last coat of resin.
I haven’t been very precise with the MEK could that be the issue?
Please be more precise. In general 1,5-2,5% of MEKP is the standard.
Any less, and you might experience undercured parts, any more, and you will ALSO experience undercured parts.
Undercured parts + water can get cloudy.
I have not been measuring my mekp or the resin as I am just using a small amount around 1/2 oz. I shoot for 1.5 to 2.5% mekp.
If the resin isn’t fully cured will it still be rock hard?
This will really not help… I had some very thin resin with a 1% hardener requirement and I measured it for volume so 100ml of resin to 1ml of hardener… It didnt work too well… It has to be by weight and since I got some accurate scales I have not had a problem with curing… Apart from once or twice with a deep mould when styrene was sitting in there and it didnt cure at all but the rest of it was perfect…